Power-generation characteristics of rechargeable direct carbon fuel cells (RDCFCs) using carbon fuel charged by methane were studied for various charging times, anode thicknesses, and flow rates of the charging gas. With increasing charging time, the power-generation capacity increased and the power density was relatively constant. The power density at the beginning of power generation did not strongly depend on the thickness of the anode. The power-generation capacity increased with increasing anode thickness from 12 to 27 mu m. The following three conclusions were obtained based on the results: (i) the anode overpotential at the beginning of the power generation did not depend on the amount of charged carbon, (ii) the effective anode thickness of electrochemical reaction was smaller than 12 mu m in this study, and (iii) the effective thickness of Boudouard corrosion was larger than 12 mu m. Therefore, the RDCFC with an anode thicker than 12 mu m should have a larger power-generation capacity while maintaining a constant power density. The power-generation capacity could be increased with decreasing flow rate of charging gas. The utilization of carbon fuel was about 46-57% in this study. (c) 2008 The Electrochemical Society.